The use of oil shale ash in Portland cement concrete Mohammad M. Smadi * , Rami H. Haddad Civil Engineering Department, Jordan University of Science and Technology, P.O. Box 3030, Irbid, Jordan Received 3 November 2000; accepted 11 July 2001 Abstract An experimental investigation was undertaken to study the potential use of Jordanian oil shale ash (OSA) as a raw material or an additive to Portland cement mortar and concrete. Different series of mortar and concrete mixtures were prepared at different water to binder ratios, and different OSA replacements of cement and/or sand. The compressive strength of mortar and concrete speci- mens, cured in water at 23 °C, was determined over different curing periods which ranged from 3 to 90 days. The results of these tests were subjected to a statistical analysis. Equations were developed by regression analysis techniques to relate the effect of batch constituents on the strength developments of OSA mortars and concretes. The models were checked for accuracy by comparing their predictions with actual test results. The obtained results indicated that OSA replacement of cement, sand or both by about 10% (by wt) would yield the optimum compressive strength, and that its replacement of cement by up to 30% would not reduce its compressive strength, significantly. It was found that OSA on its own possesses a limited cementitious value and that its contribution to mortar or concrete comes through its involvement in the pozzolanic reactions. The statistical model developed showed an excellent predictability of the compressive strength for mortar and concrete mixes. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Cement concrete; Oil shale ash; OSA 1. Introduction The use of oil shale as a source of energy has been on the rise since more than two decades. It has been used in countries such as USA, resolved USSR states, Germany, and China, while its feasibility is being studied in other countries [1]. The use of oil shale is accompanied with a by-product known universally as oil shale ash (OSA). Since the latter causes environmental problems and be- cause the cost of its disposal is very expensive, attempts were made to benefit from such material, especially in concrete and asphalt pavement construction [1–7]. The usage of the ash in concrete industry will not only reduce its production cost but also may enhance its fresh and hardened properties. Previous research concerned with this type of ash stated that its composition and properties can vary widely, ranging from high SiO 2 content, which is only pozzolanic in nature, to high CaO content which has cementitious properties on its own [1]. In view of this, there was a need to evaluate OSA pastes mechanical behavior, chemical composition, and mi- crostructure. Several studies were concerned with the mechanical behavior and microstructure of an OSA cement paste [2–5]. The findings indicated that oil ash burnt at tem- peratures which ranged from 600 to 800 °C would have a cementing strength. It was reported that the strength development rate of OSA pastes was similar to that of ordinary Portland cement, although its strength was lower owing to the extra water content added to achieve proper workability due to the higher specific surface of the OSA. The ash was also used as an additive to asphalt concrete and proved to impart better mechanical and durability performance to the mixture [6,7]. InviewofthefactthatJordanhasalargereserveofoil shale rocks, interest has increased in using such rocks as a new source of energy. After carrying out compre- hensive feasibility studies on the extraction of oil from oil shale rocks, the government has signed agreements with international companies to carry out the mining * Corresponding author. Tel.: +962-2-295-111x2145; fax: +962-2- 295-018. E-mail address: msmadi@just.edu.jo (M.M. Smadi). 0958-9465/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0958-9465(01)00054-3 Cement & Concrete Composites 25 (2003) 43–50 www.elsevier.com/locate/cemconcomp